The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Ionized gas, or plasma, is commonly used during the processing and fabrication of semiconductor devices. For example, plasma can be used to etch or remove material from a substrate such as a semiconductor wafer, and to sputter or deposit material onto the substrate. Creating plasma for use in manufacturing or fabrication processes typically begins by introducing process gases into a processing chamber. The substrate is disposed in the processing chamber on a substrate support such as an electrostatic chuck or a pedestal.
The processing chamber may include a transformer coupled plasma (TCP) reactor coil. A radio frequency (RF) signal, supplied by a power supply, is supplied to the TCP reactor coil. A dielectric window, constructed of a material such as ceramic, is incorporated into an upper surface of the processing chamber. The dielectric window allows the RF signal from the TCP reactor coil to be transmitted into the interior of the processing chamber. The RF signal excites gas molecules within the processing chamber to generate plasma.
The plasma includes electrons and positively charged particles. The electrons, being lighter than the positively charged particles, tend to migrate more readily, causing a sheath to form at surfaces of the processing chamber. A self-biasing effect causes a net negative charge at inner surfaces of the processing chamber. This net negative charge is provided relative to ground (referred to as a direct current (DC) bias) and relative to a potential of the plasma (referred to as DC sheath potential). The DC bias is a difference in electrical potential between a surface within the processing chamber and ground. The DC sheath potential is a difference between the potential of the surface within the processing chamber and the potential of the plasma. The DC sheath potential causes the heavier positively charged particles to be attracted towards the inner surfaces of the processing chamber. Strength of this DC sheath potential at the substrate largely determines the energy with which the positively charged particles strike the substrate. This energy affects process characteristics such as an etch rate or a deposition rate.
A bias RF power source supplies a biasing RF signal to the substrate support. The biasing RF signal can be used to increase the DC bias and/or the DC sheath potential to increase the energy with which the charged particles strike the substrate. Variations in the biasing RF signal produce corresponding variations in the DC bias and/or DC sheath potential at the substrate affecting the process characteristics.
A pickup device may be attached to the substrate support and is used to detect an RF peak voltage at the substrate support. A RF voltage sensor is connected to the pickup device and detects the RF peak voltage. The biasing RF signal may be adjusted based on the detected RF peak voltage to minimize variations in the DC bias and/or the DC sheath potential at the substrate.